The present invention relates to sound absorption barriers and, more particularly, to an improved panel construction adapted, in association with other similar panels, to form a sound absorption barrier. The present invention has been developed particularly for use in controlling noise generated by road or other ground transport machines but it will be apparent from the following that the invention could well be used in other applications. Situations other than adjacent roadways where the invention could be employed include industrial applications where noisy machines are used, enclosures around generators, sound barriers at airports and adjacent railway lines. Again, this list should not be regarded as exhaustive.
Unwanted sound is commonly referred to as noise. This can take the form of aircraft noise, train noise, motor vehicle noise and even loud music can be noise to some people. The level where sound becomes noise can be very subjective. At a certain level some individuals can be severely affected while other people may not react until the noise level becomes much greater. Road traffic noise generated by cars, trucks and motorcycles can take two main forms, continuous background noise and individual vehicle noise. Noise associated with heavily trafficked freeways and arterial roads is a mix of many sources, and is mainly continuous bulk traffic noise with an overlay of individual noisy vehicles.
The object of the present invention is to create a panel adapted for use in a barrier which will absorb noise from any desired location and will not reflect such noise to any significant extent while reducing such transmitted noise.
Plain, hard, dense noise barriers inserted between the noise source and the receiver, tend to reduce the transmission of noise between the source and the receiver. The insertion loss is not only dependent upon the barrier density but also the barrier height and length. The barrier integrity is important, as porous or badly joined barriers will leak noise, increasing the level at the receiver. A well constructed hard barrier will reflect traffic noise back towards and beyond the motor vehicle source. In some circumstances this may increase the noise levels at a second receiver opposite the noise barrier across the arterial road or freeway. If this occurs it may be necessary to erect a second noise barrier to protect the second receiver, resulting in parallel barriers on the sides of the roadway. The presence of high parallel reflective barriers adjacent to the roadway, can cause the multiple reflection of traffic noise between the barriers. In some circumstances the noise levels between the barriers could be higher than noise levels at the source without the barriers. If the noise level at the source is effectively increased then the noise level at the receiver will be proportionately increased. What this means, is that the erection of a second barrier will be detrimental to the receiver behind the first barrier which shields it from direct traffic noise.
The reduction of the reflection capabilities of a noise barrier will lower noise levels opposite the barrier in the single barrier situation and the noise levels on both sides of the road in the parallel barrier situation. Reducing the reflection potential of a barrier involves increasing the absorption qualities of that barrier. An absorptive barrier must also be dense enough to achieve an effective sound transmission loss through it.
Noise absorption and to a much lesser degree noise reflection is frequency dependent. Absorption co-efficients are expressed in a range of 0.0 to 1.0 at a specific frequency, normally octave or third octave points. Traffic noise is louder in the low frequency range of 100 Hz to 1000 Hz, so for an absorption barrier to be effective it must perform very well in this range.
The principle function of a sound barrier, particularly for use adjacent roadways or the like, is to attenuate noise between the source and a receiver while minimizing or proventing reflection of the noise. In achieving this basic requirement it is of course also desirable to achieve a sound barrier which is relatively inexpensive to produce, durable, maintenance free, aesthetically acceptable and has high absorption coefficients at low frequencies.